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AC wont turn on, any common thing I should check?


DonutHands
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Well this is lame, AC used to click on, but pulley was noisy as all hell and didn't blow cold. A mechanic decided to remove the belt for me while they were dealing with a suspension issue a while back.

So I finally replaced the AC compressor pulley, put it all back together and the AC wont turn on now. I press the button on the dash and the clutch does not engage. I also do not have a light on the AC dash button, although the dials do light up for vent selection/temp/speed.

After going down the wrong rabbit hole for a bit, i decided to pull the fuse, which looks good. I then pulled the relay in the engine bay and jumped the contacts and the AC clutch engages perfectly. 

 

I suppose I should go out and see if there is a matching relay to swap in to test that first, but if thats not it, any obvious places to check? Could the mechanic have disabled the AC from coming on somewhere else since they removed the belt?

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Clutch engages just fine when relay is bypassed. The issue is when the AC is turned on from the cabin climate controls the clutch/compressor is not turned on.

Im mechanically sound, something is up with the electrical side.

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I doubt the mechanic would've disabled it elsewhere. Could be that the refrigerant charge has leaked down enough over time that the low-pressure switch won't let the compressor kick on. I don't know why that would stop the light in the button from coming on, though. Could be that's on the circuit controlled by the pressure switch, or you could be correct about an electrical fault elsewhere that just isn't telling the aircon to engage in the first place. I wouldn't expect a faulty relay to explain the light not coming on, but I don't know how Nissan wired it up. The service manual should have the wiring diagram (probably in HA, if not try EL), and some troubleshooting ideas as well.

 

My first check would be shorting out the low pressure switch. If the compressor starts with that bypassed, that's a pretty good sign that the gas is low and needs to be refilled (and the leak fixed, if you can find it). If you've got no voltage across the low pressure switch, you've got an electrical fault elsewhere.

Edited by Slartibartfast
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Building off of @Slartibartfast, I would lean towards low pressure...  in my personal experience, that has always been the issue, on multiple vehicles, but YMMV. As for the light, in my '88 (not sure about '97s) the light does not turn on unless the clutch is electrically engaged. Meaning no light if the system pressure is below the pressure switches minimum threshhoold.

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